Recent pending regulations for controlling the emission of fuel vapors have required installation of fuel vapor emission control devices to limit escape of fuel vapors through the engine air inlet during periods when the engine is not operating and provide a purging mechanism that operates when the engine is running. This recently imposed requirement on small engine manufacturers has created problems in installing the engines in the equipment in which they are to be used inasmuch as the equipment manufacturer commonly purchases the engine and fuel tank for installation as a subassembly during final assembly of the engine operated equipment. Thus, the burden of providing fuel vapor emission control for these applications has been imposed upon the small engine manufacturer and has created problems in the design and installation of the tank and fuel system for the small engines.
Recapturing running loss evaporative emissions is one way to meet these pending regulations. During purging, vacuum forces pull vapor in the fuel tank into the manifold so that the vapors can be burned in the engine. However, the vacuum forces may be so great that it creates a high vacuum pressure state in the fuel tank, starving the engine of fuel.
There is a desire for a vapor control system that can recapture running loss evaporative emissions without causing the engine to stall because of insufficient fuel.